Shortest Reaction Time - Siemens SIMATIC S7-400 Reference Manual

Shortest Reaction Time

The following figure illustrates the conditions under which the shortest reaction
time is achieved.
SCC (OS)
PIQ
PII
User program
SCC (OS)
PIQ
Figure 3-8 Shortest Reaction Time
Calculation
The (shortest) reaction time is made up as follows:
• 1 × process image transfer time of the inputs +
• 1 × process image transfer time of the outputs +
• 1 × program processing time +
• 1 × operating system processing time at SCC +
• Delay in the inputs and outputs
This is equivalent to the sum of the cycle time and the delay in the inputs and
outputs.
Note
If the CPU and signal module are not in the central rack, you have to add double
the runtime of the DP slave frame (including processing in the DP master).
Automation System S7-400 CPU Specifications
A5E00165965-01
Delay of the inputs
Immediately before the PII is read in, the status of the input under
review changes. The change of input signal is also taken into account
in the PII.
The change of input signal is processed here by the user program.
The reaction of the user program to the change of input signal is output
here to the outputs.
Delay of the outputs
Cycle and Reaction Times of the S7-400
3-15